Valve controlled coating material heating unit



1954 c. B. LANSING ET AL 2,670,233

VALVE CONTROLLED COATING MATERIAL HEATING UNIT 2 Sheets-Speet 1 FiledMay 22, 1950 B. LANSING G. HART CHARLES EDWARD y VALVE CONTROLLEDCOATING MATERIAL HEATING UNIT 2 Sheets-Sheet 2 Filed May 22, 1950 lbsIOI

, Zhwentor CHARLES 5R LANSING EDWARD 6;. HA

Gttorneg Patented Feb. 23, 1954 VALVE CONTROLLED COATING MATERIALHEATING UNIT Charles B. Lansing and Edward G. Hart, Cleveland, ()hio,assignors to The Arco Company, Cleveland, Ohio, a corporation of OhioApplication May 22, 1950, Serial No.-163,512

8 Claims.

This invention relates to the heatingof coating materials prior tospraying and more particularly to a coating material heating unitutilizing steam. as its source of thermal energy and having a steam flowregulating mechanism.

Since low pressure steam providesa relatively low temperature heatsource, capable of deliverin a large volume of B. t. u.s withoutcreating a fire hazard with volatile solvents, it is the most desirablemedium for heating heavily pigmented coating materials. A furtherimportant advantage of steam is the fact that the'entire heating unitmay be simple, light, compact and constructed entirely of parts andmaterials adapted to endure long, rough usage. The temperature of thecoating material must not exceed 220 dedegrees Fahrenheit and themaximum temperature of the steam at so pounds per square inch gauge isapproximately 250 degrees Fahrenheit.

Therefore, low-pressure steam, as a heat source,

requires only a minor regulation to prevent scorching or polymerizationof the coating material, particularly as compared to other manuallyportable heat sources such as electrical energy. Thus, low-pressuresteam is particularly adapted to the heating of heavily pigmentedcoating materials prior to spraying as a means of reducing the viscosityof these coating materials to permit applications of thick coats of thematerials without slumping.

Coating materials applied in such a manner that they provide a smoothcoat of substantially uniform thickness. When the coating material isapplied cold, that is, at normal room temperature of 60 degrees to 70degrees Fahrenheit, it is necessary to dilute these coating materialswith at least an equal quantity of solvent to permit spraying. Thisreduces the viscosity of the material to a point suitable for spraying.However, since the coating material has been thinned :by the solvent, aseries of thin coats must be applied to obtain a film of satisfactorythickness. If it is attempted to apply, as a single coat, the quantityof material involved in these several coats, the result will beunsatisfactory because of slumping, producing undesirable ridges ofmaterial. The temperature of the coating material, as sprayed, issubstantially the same as the surface upon which it w deposited.Therefore, there is insufficient cooling to heavy up the coatingmaterial before it can slump. Further, the rate of vaporization of thesolvent is too slow to increase the viscosity before slumping can occur.If, to prevent this-slumping, the proportion of solvents such aslacquers must be is reduced, the viscosity of the coating materialincreases such that the spray gun is unableto properly atomize thecoating material, resulting in blobs and mounds on the surface. Thus,the application of heavy casts of these coating materials at roomtemperature is limited to an operation consisting of the successiveapplication of a number of thin coats dure through the steps ofatomization and de-.-

posit. The heated coating material will be sulficiently fiowable to forma film of substantially thickness on the surface, yet the increase inviscosity after deposit will be sufliciently constant accelerated toprevent slumping.

This rapid increase in coating material results the coating material andvents. Since the coating an elevated temperature, the thermal cliiferenetial between the coating material and the surface to which it is appliedwill cause rapid absorption of the coating materials heat by thesurface. Since the low viscosity of the coating material is due entirelyto heat rather than additional solvents,this cooling will rapidly infromboth cooling of evaporation of the solmaterial is applied at crease theviscosity of the coating material to substantially that of the undilutedcold coating material. In addition, the elevated temperature of thecoating material will cause some of the solvents to vaporize rapidly,further increasing, the coating materials viscosity. In. practice,"

tion permits the same film thickness of coating" material to be appliedin a single application as may be appliedin several coats whenxusedcold.

of material being deposited time it is being atomized and the coatingmaterial, thus, the vis viscosity of v the heated the solvents effectsthe flow stabilization of the Although the heating of coating materials,prior to application, has proved to be a solution for the problem ofsuccessfully applying thick coating of the material in a singleapplication, the mechanics by which this is accomplished has remained amajor obstacle. The temperature to which coating materials of this typeand particularly lacquers may within a relatively narrow, criticalrange. Above this critical range the heat deteriorates the coatingmaterial, and in some cases the volatilization of the solvents becomesso rapid that insufiicient flow occurs to obtain a coating of constantthickness. Below this critical range the coating material is too viscousto be properly sprayedand insuificient flow occurs to provide a smoothfilm. Further, temperatures above the critical range may result inchemical modification of the coating material, rendering it unfit as acoating material.

The problem of maintaining the coating materials temperature within thecritical range is complicated by'the fact that, normally, the coatingmaterials are intermittently applied. Thus, the number of B. t.- u-.snecessary to maintain the coating material within the prescribedtemper'ature limits varies through a wide range. To avoid overheatingand underheating under such circumstances. the heating means must be onehaving a maximum temperature not greatly in excess of the upper limit ofthe critical range even though the flow of coating material isstopped'foran appreciable length of time. At the same time, the heatingelement must be capable of delivering adequate B. t. u.s to heat thecoating material to temperatures within the critical range even thoughthe sprayer is being used for an indefinite extended period at maximumflow capacity.

Further, the heating of materials containing volatile solvents by meansof heating elements having a temperature equal to or above the ignitionpoint of these solvents involves a serious fire hazard. This is true ofelectrical heating elements, even when they are constructed with thebest of spark and hot wire' control equipment. Steam or'organic fluidshaving substantially' the same specific heat, do not involve this firehazard. Therefore, all of the fire precautionary' equipment necessarywith-the conventional types of heaters for coating materials may beeliminated by use of our invention.

In our copendingapplication entitled Insta-ntaneous Coating MaterialHeating Unit, Serial Number l34,535-, filed December 22, 1949, and ourapplication entitled Coating Material- Hea'ting Unit, we have describeda coating ma-- terial heating unit utilizing steam as its source ofthermal energy in which overheating iscontrolled either by predeterminedtotal area of heat exchange surface or a combination of the area of heatexchange surface and evacuation of the heating chamber. Although suchdesigns provide" an effective, lightweight heating unit, each unit islimited to a predetermined range of steam pressure. Whereitis desired toprovide a unit in whichthesteam pressure may be var ied beyond thepredetermined narrow limits or to construct a' unit in which the totaleffective heat exchange area is in excess of that by which thesetemperature limits may be maintained solely by the heat exchange area,it is necessary that other means of thermal regulation be employed. Inselectingathis additional means of regulatior'nit is essentialthat thebeheated must be held meansbe compact;

simple and light in weight. By placing a valve in the steam intake line,the operation of which is coordinated to the operation of the spray gun,this regulation may be obtained. Such an arrangement may be designed tobe simple and light in weight.

"Therefore, it is a primary object of our invention to provide acompact, portable, coating material heating unit in which the quantum ofthermal energy delivered to the coating material is coordinated to theintermittent operation of thespray gun.

It is a further object of our invention to provide alightweight steamflow regulating mechamsm.

It is a still further object of our invention to provide a heating unitwhich cannot scorch the coating material or heat it to itspolymerization temperature even though the spray gun is not used for anextended period.

It is an additional object of our invention to provide a steam flowregulating mechanism de signed to withstand long and rough usage.

Other objects and purposes of our invention will be immediately seen bythose acquainted with the spraying art upon reading the followingspecification and the accompanying drawings.

Figure l is a side elevational view of our valve controlled coatingmaterial heating unit.

Figure 2 is a side elevation view of our valve controlled coatingmaterial heating unit showing the valve mechanism in central section andremoving the shell of the heat exchange element to expose its internalstructure and showing the valve in closed position.

Figure 3 is a sectional view of our valve controlled coating materialheating unit taken along the plane III-HI of Figure 1.

Figure 4 is a fragmentary sectional view of our valve controlled coatingmaterial heating unit showing the valve in open position.

Figure 5 is a fragmentary top view of our valve controlled coatingmaterial heating unit taken along the plane V--V of Figure 1.

'Figure 6 is a fragmentary, partially broken, side elevation of amodification of our valve controlled coating material heating unit.

Figure 7 is an enlarged, sectional, fragmentary, side elevation view ofthe joint between the valve and the thermostat of our modified valvecontrolled coating material heating unit.

Figure 8 is a fragmentary top view of our modified valve controlledcoating material heat ing unit.

Figure 9 is a fragmentary, broken side elevation view of a furthermodification of our valve controlled coating material heating unit.

In executing the objects and purposes of our invention we have provideda coating material heating unit in which the coating material is heatedby means of steam. The heating unit is equippedwith a valve in the steamsupply line to coordinate the flow of steam with the amount of coatingmaterial demanded by the spray gun. V

I. Valve operated by spray gun trigger Referring to the drawings ingreater detail, the numeral I indicates a spray gun having a coatingmaterial heating unit 2 mounted thereon by means of a bracket 3 and athreaded fitting 4. The heating unit 2 operates as a heat exchangerwherein the coating material is heated by lowpressure steam. The heatingunit consists of an inner shell 5 surrounded by a layer of insulation 8andaprotective-covering I. The insulation 6 may be cork, asbestos, orany other suitable insulating material. The covering 1 may be tape,rubber, plastic, or any suitable, wear resistant material for protectingthe insulation 6. At each end of and within the inner shell are a pairof spaced baffles 3, defining a first compartment 8 at-the inlet end ofthe heating unit 2 and a second compartment It at the outlet end of theheating unit 2. A plurality of tubes I I extend between and communicatewith each of the com: 'partments 9 and I0.

The tubes II, between the compartments 9 and I0, pass through thechamber I2, occupying the central portion of the heating u t 2.

A threaded hose connection I3 communicates with the first compartment 9and projects. outwardly from the heating unit 2 to receive a coat.- ingmaterial supply hose I4. A short pipe I5, associated with the threadedfitting l, communicates with the second compartment I I and providesmeans whereby the coating material is conducted from the heating-unit 2to the intake port of the spray gun I.

Steam is admitted to the chamber I2 by means of the passage I6. Thepassage I6 is formed by the tube 3d at the intake end and by the valvehousing It at the discharge end. The tube 34 is mounted on the upperside of the heating unit 2 and extends along the heating unit from theforward orintake end of the heating unit 2 to a point where it entersthe valve housing It. At the discharge end of the passage I 6 the valvehousing I8 is equipped with an annular projection for carrying thepassage I8 into the chamber I2. Adjacent the point where the passage I5terminates in the chamber I2, a valve I1 is provided in the passage I6.The valve consists of a housing I8 having a central opening I9 extendingthrough it at an angle sharply intersecting the passage I 6. The upperportion of the central opening I9 enters a counterbore in which isseated a spring 2 I.

' A valve stem 22 extends concentrically through the counterbore 20 andthe central opening I9. The valve stem 22 is of such size that it mayseat within the central opening I9 with only suflicient clearance topermit reciprocating sliding movement therethrough without binding. Apacking gland 23 surrounds the valve stem 22 and threadedly engages theopen end of the counterbore 20. The upper end of the valve stem 22 isequipped with a head 24 rigidly attached to the valve stem. A washer 25,rigidly attached to the valve stem 22, near the bottom of thecounterbore 20 when the valve is in closed position, provides a bearingmember for one end of the spring 2|. The other end of the spring 2|bears against the washer 36.

The valve stem 22, in closed position, passes through the passage It toshut off the flow of steam to the chamber I2. The valve I1 is maintainedin a closed position by the spring 2| and can be opened only by liftingthe valve stem 22 against the urging of the spring 2 I.

A substantially H-shaped arm 26 is pivotally mounted on the trigger 21of the spray gun I by the pin 28. One of bifurcated ends of the arm 26embraces the trigger 21. The other bifucrated end of the arm 26 seatsaround the valve stem 22 between the packing gland 23 and the head 24.The valve stem 22 is loosely engaged by the arm 26 to permit relativemovement between the parts as the arm is raised and lowered and topermit the heating unit 2 to be easily removed from the spray gun I.

As the trigger 21 is moved upwardly from the position shown in Figure 1to the position shown in Figure 2, the crossbar 29 of the arm 26 engagesthe end of the trigger 2'! limiting further downward movement of the arm26 relative to the trigger 2%. After engagement has been made betweenthecrossbar 29 and the trigger 27, further upward movement of thetrigger forces the arm to raise the valve stem 22 to open the valve IT.The. movement of the trigger 2'? causes the spray gun i to operate.Thus, the admission of steam to the chamber I 2 is coordinated to theoperation of the gun, both being operative or inoperativesimultaneously.

=To permit entry of a reduced supply of steam to the chamber I2 when thevalve I? is closed, a bypass 32 is provided between the chamber I2andthe passage is on the steam supply side ofthe valve I "I. This allows alimited quantity of steam to circumvent the valve I'I at all times. Theexhaust steam and condensate are removed from the chamber I2 by the port30 extending from the chamber I2 throughthe first compartment 9. Anexhaust removal hose 3| is attached to the end of the port 30.

II. Valve operated by thermostat Cur valve control heating unit may beconstructed to be operated by means of a thermostat (Figures 6, 7, and8) rather thanmanually by means of the trigger 2'? of the spray gun I.When the thermostatically controlled valve is employed the heating unit50, to which the valve is applied, is identical to cept that the secondcompartment 5| corresponding to the second compartment In of theheatingunit 2 is increased in length to accommodate the bulb of the thermostat.An opening 52 ex-' tending through the shell 53, insulation 54 andcovering 555 communicates with the second compartment ill and is definedby an internally threaded annular collar 56. The bulb 5'! of thethermostat attached to the thermostat base 59 extends an appreciabledistance into the'second compartment 5|. The threaded engagement betweenthe collar 56 and the bulb 5'! mounts both the bulb 5'! and the base 59.The thermostat housing '60 is mounted on the base 59'and has the bellows(ii of the thermostat extending outwardly therefrom parallel to theheating unit 58. The bulb 5'1 and the bellows iii are connected by asmall tube or duct of any suitable design through the housing 68 wherebythe volatile liquid in the bulb may blow between the bulb and thebellows. The thermostat may be operated by any one of a number ofsuitable materials having a low boiling point whereby vaporization ofthe liquid by the heat of the coating material will cause the bellows BIto expand, thus converting the thermal energy into mechanical energy.The principle and operation of the thermostat is conventional,therefore, its construction need not be described in detail. I

By means of the pin 62, the bellows 6| to the valve stem 63. The bellowsEl with a tubular arm 67 for telescopically receiving the end of thevalve stem 63. A pair of diametrically opposed slots 58 in the tubulararm 67 receive the ends of the pin 62. A spring 69 (Figure 7) within thetubular arm 6?, bearing at one of its ends against the bellows El and atthe other of its ends against the valve stem {it maintains the valvestem 63 away from the bellows except when the valve stem is in fullyclosed position and the bellows 6| expands further than is necessary toclose the valve. The spring is linked the heating unit 2 ex-- isprovided 8! is of lightgauge material and is intended only to keep thevalve stem 83 from vibrating axially rather than as a means of forciblyclosing the valve as is the purpose of the spring 2i. The valve stem 63is mounted parallel to the adjacent portion of the heating unit 50 andextends into the steam conduit 58 at a sharp angle to the axis of thesteam conduit whereby it intersects the steam conduit Seat a pointadjacent the entrance of the steam conduit 58 into the heating unit 50.The steam conduit 58 is provided with a boss '64 surrounding the valvestem 63. The boss 64 is equipped with an internal counterbore whereby itmay reoelve'the packing gland 65 surrounding the valve stem 63.

The valve stem may be operated entirely by means of the mechanicalmotion of the bellows 6| or it may be provided with a spring topositively maintain the valve in one desired position except whenurgedin the opposite direction by the bellows. Whichever structure isemployed is 'a matter of choice dictated by the circumstances involvedin the particular application at hand. In the above described structuresuch a spring is not utilized and the energy for operating the valvestem is provided entirely by the bellows 6!.

When it is desiredto maintain the valve in closed position, except whenpositively urged by the bellows. into open position, the spring i! isused. Such a structure is illustrated in Figure 9 wherein the valve stem1% is held in normally closed position by the spring NH. The bellowsGlis equipped with a tubular extension Hi2 for telescopically receivingthe end of the valve stem lllll. The-extension I02 is equipped with aslot I03 for slidably receiving the pin HM mounted in the valve stemHill. The mounting of the valve stem I00 is substantially similar to themounting of the valve stem 63. The valve stem [GB is equipped with ashoulder I05 to engage the end of the spring I01. Sealing is obtained bymeans of the packing gland [06 which packing gland also acts as aretainer for the spring illl.

Coating material, by means ofthe supply hose- I4, is forced to theheating unit 2 from any suitable source as a bulk supply tank, drum orcontainer. This coating material enters the heating unit 2 at atemperature, usually normal room temperature, at which it can be forcedthrough the supply hose l4 without use of excessive pressures. Thecoating material enters the first compartment 9 bymeans of the hoseconnection l3. Thereafter it flows through the banks of tubes H in'heatexchange relationship to the steam in the chamber l2. Before the spraygun l is initially operat'ed'the valve I1 is opened a sufficient lengthof time to admit enough steam to heat the coating material to atemperature between 110 degrees Fahrenheit and 220 degrees Fahrenheit.When the initial batch of coating material in the heating unit 2 hasbeen properly heated, the spray gun is'operated'. Moving'the trigger 21to operate the spray gun forces the valve I'l into open position.Thereafter, whenever the trigger 21* is moved to operate the spray gunI, the valve I1 is openedand when the spraying is stopped the valve 11shuts off the steam supply. The valve I1 is urged into normally closedposition by the spring 21'. Thus, only when the coating material ismoving through the heating unit 2' at maximum how is the full heatingcapacity of the heating unit put into operation. Overheating duringnonspraying periods is prevented by substantially shutting off the flowof steam to the chamber 12. The coating material is maintained at anelevated temperature after the valve i! has been closed by the reducedflow of steam entering the chamber by means of the bypass 32.

The design of the arm 25 provides a simple but positive mechanical linkbetween the trigger 21 and the valve stem 22. Since the arm 26 has onlya pivoted linkage to the trigger 21 as the trigger 21 moves to closed oroil positior' jit'is' impossible for the arm to restrain the closingaction of the trigger. Further, in inoperative position both the trigger27 and the valve stem 22 are free to independently effect a tightclosing action.

II. Valve operated by thermostat The bulb 51 extend into the hot side ofthe heating unit 50 since it is mounted in the second compartment 5|. Asthe temperature of the coating material entering the second compartment5| increases, the liquid within the bulb 51 will vaporize causing thebellows 6| to expand. This, in turn, will force the valve stem 63 acrossthe steam conduit 58 shutting oil the steam. AS the temperature of thecoating material starts to decrease due to the cessation of the steamnew, the bellows tl will contract causing the valve stem 68 to open thesteam conduit 58. Thus, the temperature of the coating material ma beregulated within a narrow predeterminedthermal range. When the coatingmaterial is steadily flowing through the heating unit, the temperaturein the second compartment 5| will be lower, thus, causing the valve stem63 to be held in at least partially open, or retracted, positionsubstantially all of the time.

The temperature at which the bellows Bl will function to initiateshutting off the steam supply may be regulated by the choice of liquidused to actuate the bellows. A number of liquids are available, eachhaving a difierent boiling point, and, thus, a different temperatureoperating range. Thesame regulations may be effected by the length ofslots 68 or 183. The greater the length of the slot the greater thetemperature range within which the bellows 6| may move without effectingmovement of the valve stem 63 or I00.

In this manner the temperature of the coating material maybe maintainedwithin limits of degrees Fahrenheit and 220 degrees Fahrenheit. Thatthis thermal range be maintained is important because below 110 degreesFahrenheit the coating material will tend to slump after spraying. Above220 degrees Fahrenheit the coating material is in danger of eitherscorching or polymerizing, depending upon the type of coating materialinvolved; particularly if temperatures in this range persist for anysubstantial period of time.

220 degrees Fahrenheit define the broad range of operating temperatures.The preferred limits are between 1.25 degrees and 190 degrees F m en:

heit and-the optimum operating range is between degrees and degreesFahrenheit. Under all normal operating conditions, our heating unit,equipped with a steam regulating valve coordimated with the operation ofthe spray gun, is'c'apable of maintaining the coatingmaterial between125 degrees and degrees Fahrenheit.

A steam energized heating unit, equipped withthe-'abov'e-de'scribedsteam flow regulator valve,

The temperature limits of 110 degrees and eliminates the necessity ofdesigning each heating unit with a particular area of heat exchangesurface. Thus, a larger heating unit may be used under circumstances inwhich only a small quantity of coating material will be needed or steamat a higher pressure may be employed. By coordinating the steam flowregulation to the thermal demands of the spray gun, a simple, yetpositively controlled, heating unit is provided. Further, such a heatingunit lends itself to simple construction whereby the heating mechanismand the thermal control mechanism may both be mounted upon the spray gunwithout unduly increasing the spray guns Weight or making it awkward tomanipulate.

Since our coating material heating unit is designed to heat onlythestream of coating material actually flowing toward the spray gunrather than the bulk supply of coating material the capacity of thethermal energy source may be greatly reduced. Since the quantity ofcoating material to be heated, at any one time, issmall, the coatingmaterial responds rapidly to variations in the quantity of heat energysupplied. Thus, it is possible to regulate the coating materialstemperature within the preferred range of 125 degrees to 190 degreesFahrenheit by means of a simple mechanism capable of being mounteduponaspray gun where it may directly and positively the spray gun.

When the Spring loaded valve stem I60 is used, the valve is held innormally closed position by the spring I The valve will remain closeduntil the contraction of the bellows 6| overcomes the pressure of thespring IBI to open the valve. Thus, the spring will dampen thefluctuations of the valve stem I90 and the variations in the temperatureof the coating material will be somewhat greater than that experiencedwhen the valve is operated entirely by the mechanical action of thebellows.

When the valve is thermostatically controlled the use of a steam bypass,such as the bypass 32, used in connection with the trigger controlledvalve, is not essential because the thermostat will respond to thetemperature of the coating material to maintain it within apredetermined range. It may be used, however, where circumstancesdictate its utility.

The object of heating the coating material is to temporarily reduce itsviscosity while it is being deposited on the surface being coated, and,thereafter, to rapidly increase its viscosity to prevent excessive flow.By heating the coating material to 110 degrees Fahrenheit or more, theviscosity of the coating material is materially reduced. The rate ofviscosity reduction is greater in the range between 60 degrees and 125degrees Fahrenheit than between 125 degrees and 190 degrees Fahrenheit.Within the range of 125 degrees to 196 degrees Fahrenheit a portion ofthe solvents, especially those having a low boiling point, willvolatilize substantially immediately after deposit of the film ofcoating material. The coating material, although having a sufiiclentlylow viscosity at the nozzle of the spray gun to permit thoroughatomization, rapidly increases its viscosity due to rapid cooling andvolatilization of the solvents.

By the application of heat, the viscosity of the coating material isreduced to a point where the coating material is suitable for sprayingwithout the addition of further solvents. As the film of material formson the surface being coated it be coordinated to the operation of (iiicools rapidly by heat transfer due to the large thermal difierentialbetween the heated coating material and the surface. The cooling issufiiciently rapid to thicken the material before it can slump and formridges. Suificient flow occurs, however, to permit formation of a filmof substantially constant thickness. This cooling affects primarily thatportion of the film adjacent to the surface being coated. Flow andslumping of the exposed surface of the film is controlled by evaporationof some of the heated solvents. Since, in this manner, a coatingmaterial of high viscosity, at room temperature, may be applied to asurface and its flow regulated, it is possible to apply, in a singlecoat, the same quantity of heated coating material which can only beapplied by the use of several coats of cold coating material. This istrue since it becomesunnecessary to dilute the coating material withsolvents.

It is important that our heating unit is designed primarily to beoperated with relatively low pressure steam, i. e., steam having apressure range of 1 to 30 pounds per square inch gauge. Such pressuresdo not require heavy, pressureresisting structures. Further, the maximumtemperatures of such low pressure steam is'not greatly in excess of themaximum permissible temperature of 220 degreesFahrenheit for the coatingmaterials. At the same time low pressure steam is capable of deliveringlarge quanti ties of B. t. u.s to efiect rapid heating of the coatingmaterial. It is capable of doin this,

even though controlled by only simple regulatory means, withoutendangering the coating mate: rial immediately adjacent the heatexchange surfaces by overheating.

Modifications may be made in the exact structure employed to carry outthe principle of our. invention; however, each of such modifications areto be considered as included within the following appended claims,unless said claims by their language expressly provide otherwise.

We claim: 1. In a heating unit associated with a spray gun for heating acoating material prior to spraying, the improvement in said heating unitcomprising: a housing oblong in cross section having a curved contouraround the trigger portion of said spray gun enclosing therein a heatexchange element, said heat exchange element having a, coating materialflow capacity equal to the maximum instantaneous coating material demandof said spray gun; a first conduit for steam to said heat exchangeelement; a second conduit for continuously exhausting steam andcondensate from saidheat exchange element and to a remotely positionedheat supply reservoiri means for passing said coating material throughsaid heat exchange element in heat exchange relationship to said steam;a, valve in said first conduit; means for opening and closing said valvein coordination with the movement of said coating material through saidheat exchange element; said valve being integrated with the heatexchange element by attachment to the inner shell of said heat exchangeelement; and the whole heating unit attached to the spray gun by abracket.

2. In a heating unit for heating a coating material to a predeterminedtemperature range-between degrees and 190 degrees Fahrenheit. prior tospraying, the improvement in said heat-1 ing unit comprising: a housingoblong in cross section havin a curved contour around the trig-j gerportion of said spray? gun enclosing therein admitting ac'zoaes ll aheat-exchange element; afirst conduitior admitting steam: to said heatexchange. element; a second conduit. for continuously. exhausting steam-,and.-condensate from said heat exchange element and tea remotely;positioned heat suppiy reservoir;.means.-ior passing said coatingmaterial throughsaiduheat. exchange element inheattexchangerelationshipto said steam; a valve insaidfirst conduit;means ion-opening and closing. said. Y valve in coordination .with themovement-of. said coating material through said heat exchange element.for. maintaining said coating material within the predeterminedtemperature range of 125 to 190 degreesFahrenheit, said valve beingintegratedwith theheat exchange element by attachment to the inner shellofsaid heat exchange element; and the whole heating unit attached to thespray. gun by a bracket.

3. In a heating unit mounted upon a spray gun having a trigger, saidunit adapted for heating a coating material prior to sprayingsaid.heatingunit comprising: a housingdefining an enclosed central chamber;.a first. pipe for corn ductingsteam into said chamber; a second pipefor. conducting excess steam and. condensate out of,..said chamber;tubular means within said chamber. for passing said coating materialthrough said chamber in heat exchange relationshipto said steam; avvalve in said first pipe for controlling steam flow; resilient-meansfor urging said valve into closed position; an arm having one of itsends engaging said valve and the other of its ends engaging said triggerfor urging said valve to move in unison with said trigger whereby whensaid trigger, is moved "in a manner to cause said spray gun to. operatesaid arm moves said valve to open position said valve being integratedwith the heat exchange element by attachment to the inner shell of saidheat exchange element; and the whole heatin unit attached to the spraygun by a bracket;

4. In a heating unit=mounted upon a spray gun having a trigger, saidunit adapted for heating a coating material prior to spraying, saidheating unit comprising: a housing enclosing therein a heat exchangeelement; a first conduit for. admitting steam to said heat exchangeelement; a second conduit for exhausting steam and condensate from saidheat exchange element; means for flowing said coating material throughthe said heat exchange element in heat exchange relationship to saidsteam; a valve in saidfirst conduit; including a valve stem andmeansresiliently urging said valve stem into normally closed position; ahead on one end of said valve stem; an arm bifurcated on eachof. fitsends and having. a crossbar separating said bif-urcated ends; one end-ofsaid arm embracing. and :pivotally mounted to said trigger; the otherand f said arm embracing said valve stem and engaging said head; saidcrossbar engaging said trigger as 'said trigger is'moved in amanner to.operate said spray gun "whereby said arm and valve stemare urged 2 tomove with said triggertor opening said valve; means for supporting saidheating unit on said spray gun.

5..Inia heating element as described in claim- 4 wherein a bypassconduit is provided between said: fir'stnconduitandwsaid heatexchangeelement; .rsa'id bypass conduit communicating with said first conduit ontheside of said valve remote from said 'heat exchange element.

6. 111a heating unit mounted upon a spray gun having a trigger, saidunit. adaptedtor heating a .coatinglmaterial' prior to spraying, saidheating;.unit. comprising; a housing. enclosing=. thcre-. in a heatexchange element; a first conduit for admitting steam to said heatexchange element; a second conduit for exhausting steam and condensatefronr said heat exchange element; means for passing said coatingmaterial, through said heatex-change element in. heat exchange. relaetionship to .saidsteam; a valve insaid conduitfor;controlling-,-the.flow of steam into said heat exchange element,said valve resiliently urged into .a normally closed position; lever.meansengaging both said trigger and said valve forropening said valvesimultaneously with movement of saidtrigger to spray gun operatingposition said valve being integrated with the heat exchange element byattachment to theinner shell of said heat exchange element; and thewhole heating unit attached to the spray gun by a bracket.

'7. .In a heating unit associated with a spray gun for heating a coatingmaterial prior tospraying,. said heating unit comprising: a housingoblong in.:cross section having a curved contour around the. triggerportion of said spray: gun enclosing therein a .heat exchange element,said heat exchange element having a coating materialflow capacity equalto the maximum. instantaneous coating material demand of said spray gun;a first conduitfor admitting steam to said heat exchange element; asecond conduit for, continuously exhausting steamand condensate fromsaid heat exchange element and to a r.e-- motely positioned heat supplyreservoir; means for flowing said coating material through saidheatexchange element. inzheat exchange relationship to said steam; a valveinisa-id conduit for" controlling the flow of steam into said: heatexchangeelement; a thermostat having its heat sensitive element mountedin the coating mate'- rial discharge end of saidxheatingrunit;-. meansmounted on said thermostat for opening :and closing said valve.

8. A heating unit as described in claim-7, wherein said thermostatincludes .a bellows and said means mounted on said thermostat is mountedon said bellows and includes. a tubular element telescopically receivingone .end' of. said valve; the walls .of said tubular element defining aslot parallel-to the direction otmovement of said bellows; a pin in saidvalve -slid ably seated within said slot; a spring. within said tubularelement. for urging said valve avvayfmm said bellows whereby saidbellows may. have limited-movement while said valve is stationary.

CHARLES E. LANSING.

EDWARD. G. HART.

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